Flexible fiberoptic colonoscopy has assumed increasing clinical importance for both diagnostic and therapeutic indications. Despite numerous reports of complications associated with colonoscopy, no large body of prospectively gathered data exists to indicate the risks of this widely-used procedure. To provide this data, we plan to conduct a national prospective survey of members of the American Society for Gastrointestinal Endoscopy. Initially a data form will be developed for this purpose and tested in a small pilot survey. This will be followed by the formal national ASGE survey. Data will be computerized for subsequent simple and multivariant analysis. In addition to determining the incidence and nature of colonoscopic complications, we plan to identify clinical or procedural factors which may predispose to their occurrence. Information about current colonoscopic practices will also be collected. Identification of the factors connoting a high risk may ultimately help to reduce the complications of colonoscopy.